This application claims foreign priority from Israeli Application No. 130939 filed in Israel on Jul. 14, 1999 which application is hereby incorporated by reference as if fully set forth herein.
The present invention relates to probe devices which apply a predetermined static pressure to a body part of a patient, preferably a digit (i.e., a finger or toe) of the patient, while non-invasively detecting certain medical conditions. The invention is particularly useful in the methods and apparatus described in our PCT Application PCT/IL97/00249, published as International Publication No. WO98/04182 on Feb. 5, 1998, and in our Israel Application 124787 filed Jun. 7, 1998; and the invention is therefore described below with respect to such methods and apparatus.
Publication WO 98/04182 discloses methods and apparatus for the non-invasive detection of a change in a physiological condition of a patient by monitoring changes in the peripheral arterial tone as manifested by changes in the arterial blood volume in a terminal extremity of a body part, preferably a digit (finger or toe) of the patient. The method and apparatus are described therein particularly for detecting mycardial ischemia and sleep apnea, and also for continuously monitoring blood pressure. The preferred constructions described therein generally include a probe for application to the patient""s body part (e.g., finger). The probe includes a housing for receiving the distal end of the patient""s body part, and pressurizing means for applying a static pressure field substantially uniformly around the distal end of the patient""s body part when received in the compartment, including its terminal-most extremity. The static pressure field is of a predetermined magnitude sufficient to substantially prevent distention of the venous vasculature, uncontrolled venous backflow, and retrograde shockwave propagation into the distal end of the body part, and to partially unload the wall tension of, but not to occlude, the arteries in the distal end of the body part when at heart level or below. The probe further includes a sensor for sensing changes in the distal end of the patient""s body part related to changes in volume therein which are due to changes in instantaneous blood volume related to arterial tone.
Publication WO 98/04182 discloses various types of devices or probes which may be used, and many applications of such devices. Some of the devices measure changes in volume in the distal end of the digit accompanying blood pressure waves, while other devices measure changes in optical density in the distal end of the digit accompanying blood pressure waves.
Further information concerning the construction and operation of such devices, as well as many of the applications in which such devices may be used, appears in our Publication WO 98/04182, which is hereby incorporated herein by reference.
It was found that at times the sensors used in such devices were extremely sensitive to movements of the finger, such as finger jitter during exercise. Such movements of the finger tend to produce volume changes which could affect the accuracy of the sensor in detecting the change in the actual physiological condition of the patient being monitored.
An object of the present invention is to provide a device for application to a body part of a patient to detect a change in the physiological condition of the patient, which device exhibits less sensitivity to movements of the body part during its use. Another object of the invention is to provide a device of the foregoing type which is of a relatively simple construction, and which therefore can be produced in volume and at relatively low cost.
According to the present invention, there is provided a device for application to a body part of a patient to detect a change in the physiological condition of the patient, comprising: a housing for receiving the body part; pressurizing means for applying a pressure field around the body part when received in the housing; and a sensor for sensing changes in the body part related to changes in blood volume therein; characterized in that: the housing includes at least three contiguous but separate sections including a distal end section at its distal tip, a proximal end section at its opposite end, and at least one middle section between the end sections; and in that the pressurizing means applies a pressure field to the portions of the body part received within at least the distal end section and the middle section of the housing; and the sensor senses changes in the portion of the body part received within the middle section of the housing.
In most of the preferred embodiments of the invention described below, the pressurizing means also applies a pressure field to the proximal end section and comprises one or more deformable membranes, preferably of resilient elastomeric material, within the housing defining a separate fluid chamber within each housing section; and a fluid pressure source for applying a fluid pressure, preferably a static fluid pressure, to all the chambers.
According to further features in these preferred embodiments of the invention described below, the housing is configured to receive a digit of the patient and includes: a closed distal end, enclosing one or more chambers, for receiving the distal end of the patient""s digit; and an open proximal end, enclosing one or more additional chambers, at the opposite end of the housing and connected thereto by the middle section.
As will be described more particularly below, a device constructed in accordance with the foregoing features is less sensitive to certain movements of the patient""s body part, (e.g., a finger), during the test period. This is because the sensor measurements are taken in the area of the middle chamber which is open at both ends, and therefore longitudinal movements of the finger, (e.g., finger jitter during exercise) would tend to produce substantially equal movements at the two ends of the middle section, such that the effects of such movements on the sensor measurements taken in the middle chamber tend to cancel each other.
In one described embodiment, the housing is constituted of a plurality of parts secured together, and the chambers are also constituted of separate membranes, one secured within each of the parts. In a second described embodiment, the housing is constituted of a single part of tubular shape, and the chambers are also constituted of a single membrane of tubular shape, the device including a plurality of internal annular rings for pressing spaced annular portions of the membrane to the inner surface of the housing to define the separate fluid chambers within the housing.
A third embodiment is also described below wherein the closed distal end of the housing, and the end fluid chamber therein, are of substantially shorter length than the other portions of the housing and the fluid chambers therein. In addition, the end fluid chamber in the closed distal end section of the housing includes an abutment element having a concave surface for receiving the distal tip of the patient""s digit.
A fourth embodiment is also described below, wherein the housing is in the shape of a cylinder open at both ends, and the distal end is closed by a fluid chamber mounted therein. In one variation of this embodiment, only the fluid chamber closes the distal end of the cylinder; whereas in another variation the end fluid chamber closing the open end of the cylinder includes a rigid element mounted within the distal end of the cylinder and enclosed by the membrane defining the end fluid chamber. In the construction wherein the rigid element is enclosed by the membrane, the rigid element is formed with holes therethrough permitting the free flow of fluid within the end chamber with respect to both sides of the rigid element.
Still further embodiments are described wherein the proximal end section includes a sponge cushion rather than a pressurized chamber.
All of the foregoing embodiments may be implemented in relatively simple structures capable of being produced in volume and at a low cost.
Further features and advantages of the invention will be apparent from the description below.